1. Field of the Invention
The present invention relates to an engine start method of vehicle having starter and ISG, and more particularly to an engine start method that considers coolant temperature and a voltage of a battery so as to improve exhaust/fuel efficiency performance, and so as to prevent an excessive discharge and a reduction of service time of a battery by improving a battery discharge current profile.
2. Description of the Related Art
An electric apparatus for vehicles, generally engine electrics and light devices, such as lamps, audio systems, heaters, air conditioners, etc. are supplied with power from the battery when the vehicle is stopped and are supplied with power from an alternator when the vehicle is driving. Most systems use 14V.
However, various new technologies are recently being included in vehicles.
Therefore, an electric system which supplies more power is required. One proposed solution is a dual electric system, i.e., the electric system is duplexed into a voltage of 14V/42V. The voltage of 42V is supplied to the chassis and motor to increase power efficiency, and the conventional voltage of 14V is supplied to low-power devices.
The dual electric system is composed of an integrated starter generator(ISG) that functions as a starter motor and generates high power, a motor control unit(MCU) that accomplishes various controls of the ISG drive such as output control, starter function control, etc., a 36V battery, a battery management system(BMS) that controls the 36V battery, a 42V motor driven by the 36V battery that powers various high-power devices, a bidirectional DC/DC converter that converts the voltage supplied from the 36V battery to 12V, and a 12V battery that stores the power converted by the DC/DC converter and drives various low-power devices.
The ISG operates as a starter at the time of starting an engine and operates as an alternator at the time of normal driving of the engine.
There are proportional relationships between the engine temperature and the engine friction torque, and between the engine friction torque and the engine driving force. The force needed to drive the engine depends on the engine temperature, however this has not been taken into consideration.
Therefore, if the ISG is used at the time of starting an engine of the dual electric system vehicle, the life time of the 36V battery will be shortened considerably.
There is a need to improve exhaust/fuel efficiency performance by considering the engine temperature and the battery voltage at the same time, also the battery discharge according to the engine temperature should be taken into consideration so as to increase the life time of the 36V battery.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.